1. Field of the Invention
The various embodiments of the present invention generally relate to processes and systems for bagging pellets. More specifically, the various embodiments of the present invention relate to improvements in the processes of extruding, pelletizing, drying, and bagging of meltable and/or processable polymers, specifically those that are tacky, so as to provide processes where the meltable and/or processable polymers are extruded, pelletized, dried, and bagged continuously.
2. Description of the Prior Art
The generally independent processes of, and equipment for use in, extrusion, pelletization, drying, and bagging of polymeric material are known and have been used in various applications. Over time, the demand for processes and equipment capable of efficiently extruding, pelletizing, drying, and bagging tacky polymers (e.g., hot melt adhesives and hot melt pressure sensitive adhesives) has increased. Yet, the prior art remains silent as to a process where such materials are extruded, pelletized, dried, and bagged continuously (i.e., where such material is pelletized and flows continuously throughout the process until it is bagged).
German Patent DE 22 48 046 discloses the confectioning and packaging of thermoplastic adhesives. According to the teachings of this patent, which are widely used, a hot melt adhesive is squeeze-cut into roughly pillow-shaped pieces, the pieces are subsequently cooled (and thus solidified), are then put into sacks, cartons, and like containers for packaging. To reduce the tendency of the individual pillows to stick or to adhere to each other, an anti-stick substance (e.g., a wax or a polymer) can be used to coat them, as taught in German Patent DE 33 27 289. Another method for packaging adhesive compositions includes wrapping or placing larger portions of the adhesive in a plastic film material, such as thick polyethylene.
These existing packaging techniques suffer from drawbacks. Specifically, the adhesive composition must be removed from the packaging material prior to use, thereby requires further handling of the material. In addition, the packaging material must be discarded after emptying, which leads to material waste and expenditures for disposal of the used packaging material.
German Patents DE 31 38 22 and DE 32 34 065 disclose coating the circumference of elongated hot-melt portions with a thin polyolefin film in order to prevent sticking problems when winding these string-like portions unto each other. The portions are subsequently cut to make cartridge of cartouche fillings, whereby the film stays on the circumference and is molten and applied together with the adhesive.
The above-mentioned references relate to the concept of preventing individual hot-melt portions or pieces from sticking by individually coating them with a polymeric film. Such processes would not be practical for mass-producing thermoplastic adhesive composition pillows, since they would be very expensive to implement on an industrial scale, the desired adhesive composition would be greatly diluted with the coating film material, and the squeeze-cutting step does not allow for a complete enclosure of the individual pillows by the film.
Therefore, a need arose for a method of packaging one or more pieces of adhesive compositions that would reduce the amount of handling of the adhesive. Such a method is disclosed in U.S. Reissued Pat. No. Re. 36,177. This reference discloses a packaging material that is capable of being melted with the adhesive composition without adversely affecting the properties of the adhesive composition. That is, the packaging composition is blendable in the melted adhesive, and does not result in a deteriorated adhesive once blended therein. U.S. Reissued Pat. No. Re. 36,177, however, remains silent as to any processing conditions that are necessary to continuously bag such pelletized compositions.
Other methods for packaging tacky polymers have been developed and are widely known to those skilled in the art. One such method requires that the material be poured into a container (e.g., a plastic bag or specially designed cardboard box) in a molten state. Regardless of whether the melt is poured into a bag or a box, it must be cooled. To cool the molten polymer, which has been poured into a compatible bag, the polymer is placed into a flowing “bath” of cooling liquid. Such baths can take up a considerable amount of space and require a significant amount of energy to operate.
To package molten polymer in a box, prior art methods entail pouring the molten material into a specially designed box, such as a cardboard box with coated interior walls. Such boxes can be costly, and may only be used once. This method of boxing the molten material is not practical for a variety of reasons, including the polymeric material is exposed to contaminants, the overall method is environmentally unfriendly, it is difficult to remove the polymeric material from the box, and there is a possibility of breaks and/or leaks in the boxes during handling. Adding to the cost and inefficiency of such processes is the manner in which the melt is cooled. By placing the filled boxes on rolling trays and cooling them in large refrigerators, manufacturers are able to cool the melt, but at the expense of high electricity costs. Special release paper and plastic molds may also be used to package the material, but the paper can be costly and, in some cases, may only be used once as it must be torn to obtain the material which it surrounds. By packaging the material in special release paper it must first be cooled by way of the inefficient refrigerator method described above. Additionally, polymeric materials that are packaged in plastic molds are also cooled in a related manner.
In addition to bagging and packaging processes, the extrusion, pelletization, and drying of polymeric materials have been described elsewhere.
For example dryer equipment has been used by the assignee of the present application for many years as demonstrated in prior art disclosures including, for example, U.S. Pat. Nos. 3,458,045, 4,218,323, 4,447,325, 4,565,015, 4,896,435, 5,265,347, 5,638,606, 6,138,375, 6,237,244, 6,739,457, 6,807,748, 7,024,794, and 7,171,762; U.S. Patent Application Publication No. 2006/0130353; German Patents and Applications DE 19 53 741, DE 28 19 443, DE 43 30 078, DE 93 20 744, and DE 197 08 988; and European Patents EP 1 033 545, EP 1 123 480, EP 1 602 888, EP 1 647 788, EP 1 650 516, and EP 1 830 963.
Similarly, pelletizing equipment has been used by the assignee of the present application for many years as demonstrated in prior art disclosures including, for example, U.S. Pat. Nos. 4,123,207, 4,251,198, 4,500,271, 4,728,276, 4,888,990, 5,059,103, 5,624,688, 6,332,765, 6,551,087, 6,793,473, 6,925,741, 7,033,152, 7,172,397, 7,267,540, and 7,318,719. Similarly, die equipment and designs have been used by the assignee of the present application for many years as demonstrated in the prior art disclosures including, for example, U.S. Pat. Nos. 4,621,996, 5,403,176, 6,824,371, and 7,402,034.
Similarly, other methods and apparatuses have been developed and used by the assignee of the present application for many years as demonstrated in prior art disclosures including, for example, U.S. Patent Application Publication Nos. 2007/132134, 2009/0110833, 2007/0284771, U.S. patent application Ser. No. 12/029,963, International Patent Application Publication Nos. WO 2007/064580 and WO 2007/103509, and EP Patent Application No. EP 012 352.6. All of the above referenced patents and applications are all owned by the assignee and are included herein by way of reference in their entirety.